From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx191.postini.com [74.125.245.191]) by kanga.kvack.org (Postfix) with SMTP id D6CFB6B0002 for ; Wed, 20 Feb 2013 07:51:33 -0500 (EST) Received: by mail-qa0-f65.google.com with SMTP id j8so472511qah.8 for ; Wed, 20 Feb 2013 04:51:32 -0800 (PST) Message-ID: <5124C6CF.1020001@gmail.com> Date: Wed, 20 Feb 2013 20:51:27 +0800 From: Ric Mason MIME-Version: 1.0 Subject: Re: [patch] mm: mlock: document scary-looking stack expansion mlock chain References: <1359699013-7160-1-git-send-email-hannes@cmpxchg.org> In-Reply-To: <1359699013-7160-1-git-send-email-hannes@cmpxchg.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: Andrew Morton , Alexander Viro , Hugh Dickins , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 02/01/2013 02:10 PM, Johannes Weiner wrote: > The fact that mlock calls get_user_pages, and get_user_pages might > call mlock when expanding a stack looks like a potential recursion. Why expand stack need call mlock? I can't find it in the codes, could you point out to me? > > However, mlock makes sure the requested range is already contained > within a vma, so no stack expansion will actually happen from mlock. > > Should this ever change: the stack expansion mlocks only the newly > expanded range and so will not result in recursive expansion. > > Reported-by: Al Viro > Signed-off-by: Johannes Weiner > --- > mm/mlock.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/mlock.c b/mm/mlock.c > index b1647fb..78c4924 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -185,6 +185,10 @@ long __mlock_vma_pages_range(struct vm_area_struct *vma, > if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) > gup_flags |= FOLL_FORCE; > > + /* > + * We made sure addr is within a VMA, so the following will > + * not result in a stack expansion that recurses back here. > + */ > return __get_user_pages(current, mm, addr, nr_pages, gup_flags, > NULL, NULL, nonblocking); > } -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org